arXiv subjects

D. Schertl

Publications and source records attributed to D. Schertl.

48 records · Page 3Linked to original sources

arXiv2005

Bispectrum speckle interferometry of the massive protostellar outflow source IRAS 23151+5912

We present bispectrum speckle interferometry of the massive protostellar object IRAS 23151+5912 in the near-infrared K' band. The reconstructed image shows the diffuse nebulosity north-east of two point-like sources in unprecedented detail. The comparison of our near-infrared image with mm continuum and CO molecular line maps shows that the brighter of the two point sources lies near the center of the mm peak, indicating that it is a high-mass protostar. The nebulosity coincides with the blue-shifted molecular outflow component. The most prominent feature in the nebulosity is a bow-shock-like arc. We assume that this feature is associated with a precessing jet which has created an inward-pointed cone in the swept-up material. We present numerical jet simulations that reproduce this and several other features observed in our speckle image of the nebulosity. Our data also reveal a linear structure connecting the central point source to the extended diffuse nebulosity. This feature may represent the innermost part of a jet that drives the strong molecular outflow (PA ~80 degr) from IRAS 23151+5912. With the aid of radiative transfer calculations, we demonstrate that, in general, the observed inner structures of the circumstellar material surrounding high-mass stars are strongly influenced by the orientation and symmetry of the bipolar cavity.

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arXiv2005

High angular resolution N-band observation of the silicate carbon star IRAS08002-3803 with the VLTI/MIDI instrument

We present the results of N-band spectro-interferometric observations of the silicate carbon star IRAS08002-3803 with the MID-infrared Interferometric instrument (MIDI) at the Very Large Telescope Interferometer (VLTI) of the European Southern Observatory (ESO). The observations were carried out using two unit telescopes (UT2 and UT3) with projected baseline lengths ranging from 39 to 47 m. Our observations of IRAS08002-3803 have spatially resolved the dusty environment of a silicate carbon star for the first time and revealed an unexpected wavelength dependence of the angular size in the N band: the uniform-disk diameter is found to be constant and ~36 mas (72 Rstar) between 8 and 10 micron, while it steeply increases longward of 10 micron to reach ~53 mas (106 Rstar) at 13 micron. Model calculations with our Monte Carlo radiative transfer code show that neither spherical shell models nor axisymmetric disk models consisting of silicate grains alone can simultaneously explain the observed wavelength dependence of the visibility and the spectral energy distribution (SED). We propose that the circumstellar environment of IRAS08002-3803 may consist of two grain species coexisting in the disk: silicate and a second grain species, for which we consider amorphous carbon, large silicate grains, and metallic iron grains. Comparison of the observed visibilities and SED with our models shows that such disk models can fairly -- though not entirely satisfactorily -- reproduce the observed SED and N-band visibilities. Our MIDI observations and the radiative transfer calculations lend support to the picture where oxygen-rich material around IRAS08002-3803 is stored in a circumbinary disk surrounding the carbon-rich primary star and its putative low-luminosity companion.

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arXiv2005

First AMBER/VLTI observations of hot massive stars

AMBER is the first near infrared focal instrument of the VLTI. It combines three telescopes and produces spectrally resolved interferometric measures. This paper discusses some preliminary results of the first scientific observations of AMBER with three Unit Telescopes at medium (1500) and high (12000) spectral resolution. We derive a first set of constraints on the structure of the circumstellar material around the Wolf Rayet Gamma2 Velorum and the LBV Eta Carinae.

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arXiv2005

Close binary companions of the HAeBe stars LkHa 198, Elias 1, HK Ori and V380 Ori

We present diffraction-limited bispectrum speckle interferometry observations of four well-known Herbig Ae/Be (HAeBe) stars, LkHa 198, Elias 1, HK Ori and V380 Ori. For two of these, LkHa 198 and Elias 1, we present the first unambiguous detection of close companions. The plane of the orbit of the new LkHa 198 companion appears to be significantly inclined to the plane of the circumprimary disk, as inferred from the orientation of the outflow. We show that the Elias 1 companion may be a convective star, and suggest that it could therefore be the true origin of the X-ray emission from this object. In the cases of HK Ori and V380 Ori, we present new measurements of the relative positions of already-known companions, indicating orbital motion. For HK Ori, photometric measurements of the brightness of the individual components in four bands allowed us to decompose the system spectral energy distribution (SED) into the two separate component SEDs. The primary exhibits a strong infrared excess which suggests the presence of circumstellar material, whereas the companion can be modelled as a naked photosphere. The infrared excess of HK Ori A was found to contribute around two thirds of the total emission from this component, suggesting that accretion power contributes significantly to the flux. Submillimetre constraints mean that the circumstellar disk cannot be particularly massive, whilst the near-infrared data indicates a high accretion rate. Either the disk lifetime is very short, or the disk must be seen in an outburst phase.

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arXiv2004

Interferometric observations of the Mira star o Ceti with the VLTI/VINCI instrument in the near-infrared

We present K-band commissioning observations of the Mira star prototype o Cet obtained at the ESO Very Large Telescope Interferometer (VLTI) with the VINCI instrument and two siderostats. The observations were carried out between 2001 October and December, in 2002 January and December, and in 2003 January. Rosseland angular radii are derived from the measured visibilities by fitting theoretical visibility functions obtained from center-to-limb intensity variations (CLVs) of Mira star models (Bessel et al. 1996, Hofmann et al. 1998, Tej et al. 2003). Using the derived Rosseland angular radii and the SEDs reconstructed from available photometric and spectrophotometric data, we find effective temperatures ranging from T_eff=3192 +/- 200 K at phase phi=0.13 to 2918 +/- 183 K at phi=0.26. Comparison of these Rosseland radii, effective temperatures, and the shape of the observed visibility functions with model predictions suggests that o Cet is a fundamental mode pulsator. Furthermore, we investigated the variation of visibility function and diameter with phase. The Rosseland angular diameter of o Cet increased from 28.9 +/- 0.3 mas (corresponding to a Rosseland radius of 332 +/- 38 R_sun for a distance of D=107 +/- 12 pc) at phi=0.13 to 34.9 +/- 0.4 mas (402 +/- 46 R_sun) at phi=0.4. The error of the Rosseland linear radius almost entirely results from the error of the parallax, since the error of the angular diameter is only approximately 1 %.

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arXiv2003

Speckle interferometry of the HAeBe star V376 Cas

We report H- and K'-band speckle interferometric observations of the HAeBe star V376 Cas. Our observations show that the object is partially resolved. The visibility curves suggest three separate components: a large scattering envelope visible only in the H band, a component approximately 100 mas in radius, and a component with a Gaussian HWHM of approximately 8+/-3 mas, corresponding to approximately 5 AU at 600 pc distance, which contributes most of the flux. We compare the smallest structure to the radius of dust sublimation in the radiation field of the star and find that the radius is approximately six times larger than that expected. This may indicate that the inner regions of the system are in fact obscured by a flaring circumstellar disk or torus seen close to edge-on.

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arXiv2002

Observations of Mira stars with the IOTA/FLUOR interferometer and comparison with Mira star models

We present K'-band observations of five Mira stars with the IOTA interferometer. The interferograms were obtained with the FLUOR fiber optics beam combiner, which provides high-accuracy visibility measurements in spite of time-variable atmospheric conditions. For the M-type Miras X Oph, R Aql, RU Her, R Ser, and the C-type Mira V CrB we derived the uniform-disk diameters 11.7mas, 10.9mas, 8.4mas, 8.1mas, and 7.9mas (+/- 0.3mas), respectively. Simultaneous photometric observations yielded the bolometric fluxes. The derived angular Rosseland radii and the bolometric fluxes allowed the determination of effective temperatures. For instance, the effective temperature of R Aql was determined to be 2970 +/- 110 K. A linear Rosseland radius for R Aql of (250 +100/-60) Rsun was derived from the angular Rosseland radius of 5.5mas +/- 0.2mas and the HIPPARCOS parallax of 4.73mas +/- 1.19mas. The observations were compared with theoretical Mira star models of Bessel et al. (1996) and Hofmann et al. (1998). The effective temperatures of the M-type Miras and the linear radius of R Aql indicate fundamental mode pulsation.

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arXiv2001

Speckle interferometry and radiative transfer modelling of the Wolf-Rayet star WR 118

WR 118 is a highly evolved Wolf-Rayet star of the WC10 subtype surrounded by a permanent dust shell absorbing and re-emitting in the infrared a considerable fraction of the stellar luminosity. We present the first diffraction-limited 2.13micron speckle interferometric observations of WR 118 with 73 mas resolution. The speckle interferograms were obtained with the 6m telescope at the Special Astrophysical Observatory. The two-dimensional visibility function of the object does not show any significant deviation from circular symmetry. The visibility curve declines towards the diffraction cut-off frequency to 0.66 and can be approximated by a linear function. Radiative transfer calculations have been carried out to model the spectral energy distribution, given in the range of 0.5-25micron, and our 2.13micron visibility function, assuming spherical symmetry of the dust shell. Both can be fitted with a model containing double-sized grains (``small'' and ``large'') with the radii of a = 0.05micron and 0.38micron, and a mass fraction of the large grains greater than 65%. Alternatively, a good match can be obtained with the grain size distribution function n(a)~a^-3, with a ranging between 0.005micron and 0.6micron. At the inner boundary of the modelled dust shell (angular diameter (17 +/- 1)mas), the temperature of the smallest grains and the dust shell density are 1750K +/- 100K and (1 +/- 0.2)x10^-19 g/cm^3, respectively. The dust formation rate is found to be (1.3 +/- 0.5)x10^-7 Msol/yr assuming Vwind = 1200 km/s.

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arXiv2001

Gliese 569B: A young multiple brown dwarf system?

The nearby late M star Gliese 569B was recently found by adaptive optics imaging to be a double with separation ~1 AU. To explore the orbital motion and masses, we have undertaken a high resolution (~0.05 arcsec) astrometric study. Images were obtained over 1.5 years with bispectrum speckle interferometry at the 6.5m MMT and 6m SAO telescopes. Our data show motion corresponding to more than half the orbital period, and constrain the total mass to be > 0.115 M_solar, with a most probable value of 0.145 M_solar. Higher masses cannot be excluded without more extended observations, but from statistical analysis we find an 80% probability that the total mass is less than 0.21 M_solar. An infrared spectrum of the blended B double obtained with the MMT has been modeled as a blend of two different spectral types, chosen to be consistent with the measured J and K band brightness difference of a factor ~2. The blended fit is not nearly as good as that to a pure M8.5+ template. Therefore we hypothesize that the brighter component likely has two unresolved components with near equal masses, each the same as the fainter component. If Gl 569B is a triple our dynamical limits suggest each component has a mass of 50 (+23/-4) M_jupiter. We infer an age for the system of 300 Myr, from its kinematic motion which places its as a member of the Ursa Major moving group. All the above parameters are consistent with the latest DUSTY evolutiuon models for brown dwarfs.

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arXiv2000

Diffraction-limited bispectrum speckle interferometry and speckle polarimetry of the young bipolar outflow source S140 IRS1

We present bispectrum speckle interferometry and speckle polarimetry of the deeply embedded infrared bipolar outflow source S140 IRS1, a massive protostellar object in the L1204 molecular cloud. Using the SAO 6 m telescope, we obtained 280 mas resolution polarization maps of S140 IRS1 as well as a K-band image with diffraction-limited resolution lambda/D of 76 mas, which is the highest angular resolution image of a young outflow source ever obtained in the infrared. Our data suggest that the central source is marginally resolved with a FWHM diameter of approximately 20 mas (~ 20 AU). The most remarkable feature in our image is a bright extended and very clumpy structure pointing away from the central source in exactly the same direction as the blue-shifted CO outflow lobe. A centro-symmetric pattern of high polarization in this feature suggests that we see scattered light from the central source. We interprete this feature as the clumpy inner surface of a partially evacuated cavity in the circumstellar envelope around IRS1, which has been excavated by the strong outflow from IRS1.

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arXiv2000

GI2T/REGAIN spectro-interferometry with a new infrared beam combiner

We have built an infrared beam combiner for the GI2T/REGAIN interferometer of the Observatoire de la Cote d'Azur. The beam combiner allows us to record spectrally dispersed Michelson interference fringes in the near-infrared J-, H- or K-bands. The beam combiner has the advantage that Michelson interferograms can simultaneously be recorded in about 128 different spectral channels. The tilt of the spectrally dispersed fringes is a measure of the instantaneous optical path difference. We present the optical design of the beam combiner and GI2T/REGAIN observations of the Mira star R Cas with this beam combiner in the spectral range of 2.00 micron - 2.18 micron (observations on 22 and 25 August 1999; variability phase 0.08; V-magnitude approx. 6; seven baselines between 12m and 24m; reference stars Vega and Beta Peg). The spectrograph of the beam combiner consists of an anamorphotic cylindrical lens system, an image plane slit, and a grism. A system of digital signal processors calculates the ensemble average power spectrum of the spectrally dispersed Michelson interferograms and the instantaneous optical path difference error in real time. From the observed R Cas visibilities at baselines 12.0m, 13.8m and 13.9m, a 2.1 micron uniform-disk diameter of 25.3mas +/-3.3mas was derived. The unusually high visibility values at baselines >16m show that the stellar surface of R Cas is more complex than previously assumed. The visibility values at baselines >16m can be explained by high-contrast surface structure on the stellar surface of R Cas or other types of unexpected center-to-limb variations. The R Cas observations were compared with theoretical Mira star models yielding a linear Rosseland radius of 276Rsun +/-66Rsun and an effective temperature of 2685K+/-238K for R Cas at phase 0.08.

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arXiv2000

Observations of Mira stars with the IOTA/FLUOR interferometer and comparison with Mira star models

We present K-band observations of five Mira stars with the IOTA interferometer. The interferograms were obtained with the FLUOR fiber optics beam combiner which provides high-accuracy visibility measurements in spite of time-variable atmospheric conditions. For the Mira stars X Oph, R Aql, RU Her, R Ser, and V CrB we derived the uniform-disk diameters 11.7 mas, 10.9 mas, 8.4 mas, 8.1 mas, and 7.9 mas (+/-0.3 mas), respectively. Simultaneous photometric observations yielded the bolometric fluxes. The derived angular Rosseland radii and the bolometric fluxes allowed the determination of effective temperatures. For instance, the effective temperature of R Aql was determined to be 3072 K +/- 161 K. A Rosseland radius for R Aql of 250 Rsun +/- 63 Rsun was derived from the angular Rosseland radius of 5.5 mas +/- 0.2 mas and the HIPPARCOS parallax of 4.73 mas +/- 1.19 mas. The observations were compared with theoretical Mira star models of Bessel, Scholz and Wood (1996) and Hofmann, Scholz and Wood (1998).

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